P

Parallel

1) when 2 or more power supply outputs (of the same voltage) are connected together, +ve to +ve and -ve to -ve to increase the total output current (whilst maintaining the output voltage). Care should be taken to ensure that the power supply is suitable for parallel connection as some units will not operate well or may be destroyed by operating in this manner. Additionally, some power supplies need diodes connected in series with their outputs to operate correctly in parallel, check the operation/installation manual for details.

2) The connection of components or circuits in a shunt configuration.

Parallel Resonant Circuit

Network of resistors, a capacitor and an inductor connected as shown below.

Post Regulation

Pot

Potential Difference

(Electrical Potential Difference) – the voltage between two points causing a current to flow in a circuit.

Potentiometer (pot)

A component with an adjustable resistance (an adjustable or variable resistor).

Schematic Symbols for a Potentiometer

Potting / Potting Compound

An insulating material for encapsulating one or more circuit elements.

Powdered Iron Core

Magnetic core material that contains iron particles held together with a high resistance binder to reduce eddy currents. See also Core,Ferrite,Iron Core.

Power (P)

1) the rate of doing work, measured in watts.

2) In a resistive circuit, power is the product of the in-phase components of voltage and current (voltamperes). See also Apparent Power, True Power.

Power Cycle

A rigorous test which is designed to apply controlled strenuous test conditions to an assembled power supply, ensuring that any defects present are identified and resolved before delivery to the customer. Typically, the power cycle will operate the power supply at elevated temperature into a full load, simulating worst case conditions. The power is then turned on and off repeatedly at both high and low line input levels. It has been shown that this type of test is much more effective at discovering latent defects than the traditional burn-in procedure. See also Burn In.

Power Density

The ratio of the power available from a power source to its volume. E.g. watts/inch³.

Power Factor

The ratio of True Power to Apparent Power as a decimal, occasionally specified as lead or lag of the current relative to voltage.

Power Factor Correction

A technique to counteract the effect caused by loads that have a power factor below 1 (less than 100%). Power factor correction is necessary as it increases the efficiency of power transmission. A low power factor load increases losses in the transmission lines. Passive PFC uses an inductor to pass current at the supply frequency (usually 50Hz or 60Hz) with additional capacitors to bring the power factor close to 1. Active PFC usually employs a Boost Converter between the bridge rectifier and the reservoir capacitors to maintain the power factor close to 1. Active PFC usually provides wide range input to the power supply.

Power Fail Signal

A Status Signal from a power supply (PSU) that provides advance notice that the output voltage is about to fall out of specifications due to loss of line.

Power Source

Power Status Signals

Power Supply (PSU)

A device which supplies electrical energy to a load. Typical application of power supplies include to convert raw input power (can be either ac or dc) to a controlled or stabilised voltage and/or current for the operation of electronic equipment. Often used to convert between hazardous voltages available from wall sockets (usually 110Vac or 230Vac) to voltages which can be used by electronic equipment (CPU's, motors, telephones, etc.).

Power Supply Cord

A length of flexible cord provided with an attachment plug at one end. See also Cord Set.

Primary Winding

The driven coil in a transformer.

Printed Circuit Board (PCB)

An insulating substrate with conductive (usually copper) tracks connecting components. The PCB is used to both support and interconnect components. PCBs are made of many materials including resin impregnated paper (often called FR-2), fibreglass (FR-4), various plastics (more commonly used for high power RF circuits), ceramic or metal (usually aluminium – see IMS). PCBs can have one or more layers of copper tracks and the different layers are connected with Vias. Additional layers make the PCB cost more but have benefits (such as improving the EMC performance, improving heat conduction and reducing size).

Programmable Power Supply

A power supply (PSU) with an output (or outputs) controlled by an applied voltage, current, resistance or digital code. Lambda's ZUP and Genesys are examples of digitally, remote programmable power supplies (available with output powers from 200W up to 60kW). Lambda's Vega range is available with remote programmable output modules.

Programming

The control of a power supply (PSU) parameter, such as output voltage or Current, by means of a control element or signal (This is either done with digital control [by Communications Port] or analogue control [with resistance or voltage input to the programming pins on the power supply]).

Programming Speed

A power supply’s ability to respond to a command to change its output setting from one level to another. It can be measured in terms of a programming time constant and a slewing rate.

Programming Time

Time between the start of a programmed event and arrival within a specified range of the final value. Unless otherwise specified, 95% of the desired change should be used.

Pulse

A step rise, a level, and a step fall of voltage or current. Characteristics of a pulse are: rise time, duration (or dwell time) and fall time.

Pulse

Pulse Discharge

A non-continuous discharge.

Pulse-Width Modulation (PWM)

Regulation of the output voltage of a switched mode power supply (SMPS) by varying the duration, but not the frequency, of the pulses that drive the power switch.